One of the first shielded-base missions. This is a hard mission even with an AT-AT if you approach it the hard way. The Reinforcement Point you start with is near the northeastern coast, and the immediate road ahead next to the coast is a winding one -- which means a slow advance for walkers, and a lot of traffic jams. And as soon as you land, the Rebellion is going to come at you with a lot of artillery.

Just for fun, try it on Hard difficulty with four AT-ATs. If you just march them into the base, they can probably just take out the Shield Generator before the last of them is destroyed.

When you start, park your AT-AT near the two Building Pads, set to Vehicle Repair Stations. You don't have a lot of units to begin with, so you may want to start with an AT-AT (probably Colonel Veers), SPMA-Ts to support the AT-AT with strong long-range fire, AT-ST Walkers to use against enemies that get too close, and a Field Commander -- yes, no Darth Vader for a change.
Dig in your SPMA-Ts with the Deploy command. They don't need to undeploy and turn to fire, so they can also cover your eastern flank, whereas your AT-AT will try to turn or move.
For our strategy, you will also need at least one unit of 2-M Saber-Class Repulsor Tanks.

After you land, quickly position yourself to survive the initial onslaught. When this is over, sneak your Repulsor Tanks out onto the water off the northwest coast. If you scout along the coast, you'll find the energy generator on the south side. Take it out with your Repulsor Tanks, retreating them out onto the water whenever necessary.
Once the shield is down, you can continue to hold your position and try running a Repulsor Tank into the base to call a bombing run. If you hug the north side, you should be out of range of the coastal turrets. This is, however, a tricky proposition as your Repulsors are in trouble if they run into PLEX Troopers or MPTL-2a Artillery (PLEX ignores shields, MPTL-2a barrages take down the shields too quickly).
Have your Repulsors rejoin your main force if possible.

Next, move your force east to the next pair of side-by-side Building Pads and another Reinforcement Point. Set up Vehicle Repair Stations there to hold ground again. Call more reinforcements (e.g., Darth Vader and AT-STs to use against PLEX Troopers, which take are remarkably long time for an AT-AT to kill) and advance forward.
If you hold ground here and wait for the Rebellion to come to you, you could possibly buy your offshore Repulsor Tanks a few extra seconds to locate structures for bombing runs because they are now moving toward the path further from the coast.

Reinforcements might not be necessary, but we moved to the east because it is a straight, wide path north to the Rebel base -- no turning and traffic jams involving the AT-AT. From here, things are pretty straightforward as long as you keep your AT-AT properly covered with supporting fire. Save one Rebel structure for last (e.g., the Shield Generator or a Mining Facility) while you look for native structures to make sure you get them all for the bonus credits.